Backdrop CMS is based on the works of Drupal 7. It can be viewed as an extended version of Drupal 7 and branched off from Drupal 8 during the development cycle at a time when Drupal was getting completely refactored to include some Symfony2 framework and moving towards OOP while maintaining the Drupal UI and concepts.

Open Social is a distribution for building social communities & intranets. The distribution is positioned as the successor of Drupal Commons, taking full advantage of the new possibilities of Drupal 8.